Masterspec
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Maintaining an unobstructed ventilated drained cavity behind cladding on multi-unit/multi-storey residential or commercial buildings can be made...
18 Feb 2021
ELECTRICAL RELATED FIRES - CAN THEY BE REDUCED?
About 20% of New Zealand building fires are related to electrical systems or devices. So is there anything that could help in new builds and...
18 Feb 2021
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09 Feb 2021
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12 Jan 2021
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01 Sep 2020
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ELECTRICAL RELATED FIRES - CAN THEY BE REDUCED?

18 Feb 2021

Every year about 20% of New Zealand building fires are related to electrical systems or devices. So is there anything that could help reduce electrically related fires in new builds and retrofits. The answer is yes, the risk of fire can be reduced by using AFDDs (Arc Fault Detection Devices).

For standard (normal current, low voltage) electrical systems, an AFDD or Arc Fault Detection Device would be located in the switchboard from which the final subcircuit being protected originates. More recently RCD-AFDD combined devices (Residual Current Device plus AFDD) have become available in New Zealand, these may prove to be more popular particularly in the domestic market.

Arc Faults and Fires

Put simply, An electrical arc is an electrical current that is intentionally or unintentionally (arc fault) discharging itself across a gap between two electrodes. So, as you can imagine, arcs can generate considerable localised heat, potentially thousands of degrees (melts cable insulation), which under certain conditions may cause a fire. Arcs are normally the result of one or more of the following:
  • Cable insulation defects between live conductors (parallel arcs)
  • Broken or damaged (reduced cross-section) conductors (series arcs)
  • High resistance terminal connections
Fire ignition by arc fault can occur in the building wiring system and devices, or in connected (flexible cords/leads etc) devices and appliances. The risk of arc faults increases with; old wiring, damaged cables/cords (including rodent damage), pinched cables/cords, worn cable/cord insulation, overloaded multi boards, overheating, etc, etc. For buildings with old wiring that is not going to be replaced, adding AFDDs to the switchboard is highly recommended. It has been suggested that by adding AFDDs to old wiring could possibly help insurance issues with some companies.

Anecdotally it is said that the not insignificant cost of AFDDs (and RCD-AFDD) may be able to be offset by possible insurance cost savings (you need to check this out for yourself). But regardless, the costs would be insignificant compared to the devastation of an actual building fire caused by an arc fault.

Note; an AFDD without an RCD (Residual Current Device) or similar does not protect against sustained thermal overloads, short circuits, or residual currents. So for maximum protection, an AFDD should always be in series with a separate or combined RCD or similar.

AS/NZS 3000 Electrical installations (known as the Australian/New Zealand Wiring Rules)

NZBC G9/VM1 (A 7) cites the Electricity (Safety) Regulations 2010, which intern cites AS/NZS 3000:2007, however the latest version of the Standard AS/NZS 3000:2018 is not cited. Only AS/NZS 3000:2018 version directly refers to AFDDs in Part 2.9 and Appendix O. This means that AFDDs per se are not mandatory, although other forms of arc protection maybe required in certain circumstances under the 2007 version.

If AS/NZS 3000:2018 (clause 2.9.7) is ever cited it would make AFDDs mandatory in some circumstances for subcircuits not exceeding 20 Amps. The circumstances that are considered appropriate are:
  • Sleeping accommodation
  • Premises for the young, the elderly, the handicapped
  • Premises for large groups of people; theatres, bars, shopping malls, hospitals etc.
  • Industrial and commercial premises with increase risk; woodworking shops, barns, stores for combustible materials etc.
  • Locations and structures that are combustible etc.
  • Locations with irreplaceable contents; museums, art galleries etc.
AS/NZS 3000:2018 (clause 2.9.2) requires AFDDs to comply with IEC 62606 General Requirements For Arc Fault Detection Devices. Clause 2.9.3 requires the load current rating of the AFDD to be no less than the required RCD.

Masterspec

Masterspec, over the next few months will be adding content along the lines of this article, to all the relevant Electrical Sections.

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